NEW THEORY Olivier Theyskens debuted his Theory collection in 2010.

DYNAMIC DUO Proenza Schouler's Lazaro Hernandez (left) and Jack McCollough.

RAG & BONE

THE FASHION UPSTARTS Rosen owns a 30 percent stake in the New York City–based brand. Owners Marcus Wainwright and David Neville spend time with Rosen in his Hamptons summer home.

OLIVIER THEYSKENS

THE ARTIST IN RESIDENCE Rosen hired Theyskens after the Belgian designer fizzled at several Paris fashion houses. In 2010, Rosen named him artistic director of Theory.

PROENZA SCHOULER

THE LATEST PRIZE Last year, Rosen scored big when he led a group of investors in buying a 50 percent stake in Proenza Schouler, which won the CFDA Womenswear Designer of the Year in 2011.

HELMUT LANG

THE MINIMALISTS Husband and wife Michael and Nicole Colovos moved from Los Angeles to New York City to design Helmut Lang in 2006. They say Rosen encourages them to be true to their own voice.

ALL IN THE FAMILY Rosen's father, Carl (right, in a picture that hangs in his son's study) helped pioneer designer jeans with Calvin Klein.

Rosen with children Austin and Ashley. Austin, a fourth-generation garmento, has worked at Rag & Bone and Theory.

THE KING AT PLAY Rosen picked up his father's love of horse racing.

When he first met designer Jenny Dyer (below), he asked her to the races. They now live together.

OFFICE SPACE Rosen's HQ is in Manhattan's Meatpacking District, in a building he had the foresight to move into before the area became a shopping and nightlife mecca. On the ground floor is the flagship retail store for Theory.